Device for admixing a processing agent into a pulp suspension

ABSTRACT

Mixing devices for mixing a processing agent with a pulp suspension are disclosed including a mixing vessel, an agitator mounted on the surface of the mixing vessel to create a flow of the pulp suspension across the mixing vessel, a processing agent supply for supplying processing agent to the flow of pulp suspension, and a flow divider mounted on the inner surface of the mixing vessel opposite the agitator, in which the flow divider includes a substantially vertical front distribution edge and a pair of arcuate front surfaces extending from that edge to the inner surface of the mixing vessel on opposite sides thereof.

FIELD OF THE INVENTION

The present invention relates to a device for admixing a processingagent into a pulp suspension in a vessel. More, particularly, thepresent invention relates to such a device in which the processing agentcan consist of liquids and chemicals, substantially in a fluid state,which can be used for dilution or other types of processing.

BACKGROUND OF THE INVENTION

It is of decisive importance to obtain persistently uniform andproportional admixture of the processing agent with the pulp if onewishes to achieve acceptable results in various types of pulpprocessing.

In those arrangements which are presently utilized, the processing agentis mixed together in the lower portion of a pulp vessel. The pulpconcentration in the pulp vessel is normally between about 10 and 20%,which must be lowered to about 2.5 and 8% in order to make it possibleto pump the pulp suspension out of the vessel. When the pulp vessel isused as a bleaching tower, it is then necessary to supply a dilutionfluid through a number of nozzles in a restricted lower portion of thetower. The bottom zone of the tower in such a case is restricted by acylindrical cone in order to guide the processing agent in a circularmanner.

The use of a high pulp concentration, for example, of about 12%, in thevessel renders it problematic to achieve a uniform admixture. In orderto reduce this problem, the size of the vessel has generally beenreduced. However, such an arrangement nevertheless requires considerableenergy, due to incomplete admixture techniques and to an unsuitableconfiguration of the bottom of the vessel.

SUMMARY OF THE INVENTION

In accordance with the present invention, these and other problems havenow been overcome, and the supply and central distribution of theprocessing agent, as well as the flow of the suspension, has beenimproved. Thus, improved mixing results can now be achieved while, atthe same time, energy consumption can be lowered to a minimum value.

In accordance with the present invention, this is accomplished by thediscovery of a mixing device for mixing a processing agent with asuspension comprising a mixing vessel having an inner surface andincluding a lower cylindrical portion having a diameter, an agitatormounted with respect to the inner surface of the mixing vessel forcreating a flow of the pulp suspension across the mixing vessel,processing agent supply means for supplying the processing agent to theflow of the pulp suspension across the mixing vessel, and a flow dividermounted with respect to the inner surface of the mixing vessel at alocation substantially opposite the location of the agitator, the flowdivider comprising a substantially vertical front distribution edgespaced from the inner surface of the mixing vessel and a pair of arcuatefront surfaces extending from the front distribution edge to the innersurface of the mixing vessel on opposite sides of the front distributionedge.

In accordance with a preferred embodiment, the pair of arcuate frontsurfaces are substantially vertical.

In accordance with one embodiment of the mixing device of the presentinvention, the suspension comprises a pulp suspension. In a preferredembodiment, the pair of arcuate front surfaces extend to the innersurface of the mixing vessel substantially tangentially.

In accordance with another embodiment of the mixing device of thepresent invention, the front distribution edge is directly opposite theagitator. In a preferred embodiment, the front distribution edge islocated on a diameter of the mixing vessel, and the pair of arcuatefront surfaces comprise cylindrical surfaces having a predeterminedradius. In a preferred embodiment, the predetermined radius is betweenabout 20 and 25% of the diameter of the mixing vessel.

In accordance with another embodiment of the mixing device of thepresent invention, the pair of arcuate front surfaces include an uppersurface defining an inclined plane with respect to the inner surface ofthe mixing vessel. Preferably, the front distribution edge has a height,which is between about 10 and 20% of the diameter of the mixing vessel.Preferably, the upper surface of the pair of arcuate front surfaces havea maximum height which is between about 40 and 60% of the diameter ofthe mixing vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully appreciated with reference tothe following detailed description, which, in turn, refers to theFigures, in which:

FIG. 1 is a top elevational view showing the lower portion of a mixingvessel in accordance with the present invention;

FIG. 2 is a side, sectional, partially perspective view of the mixingvessel shown in FIG. 1 taken along lines II--II thereof;

FIG. 3 is a top schematic representation of another mixing vessel inaccordance with the present invention; and

FIG. 4 is a side perspective schematic representation of a mixing vesselin accordance with the present invention.

DETAILED DESCRIPTION

Referring to the Figures, in which like reference numerals refer to likeelements thereof, the mixing vessel according to FIG. 1 comprises acylindrical lower portion 10. An agitator 11 is fitted into the wall ofthe lower portion of the vessel. The agitator 11 comprises a propeller12, which is intended to establish a pulp flow across the vessel portion10 simultaneously as a processing agent is supplied to the pulp flow.According to the embodiment shown therein, the processing agent issupplied through a pipe 13 located above the suction side of theagitator 11, and an inclined screen 14 is located in the vessel abovethe pipe 13. Screen 14 is intended to distribute the ingoing processingagent on the suction side of the agitator 11, and at the same time toprevent air from being sucked in from the surface of the pulp suspensionin the vessel. There is a risk of air being sucked in when the level inthe vessel approaches the level of the agitator.

As an alternative, the propeller agitator can be designed in a differentmanner, for example as shown in Swedish Patent Application No.9202011-4.

Diametrically opposite the agitator 11, the lower portion 10 of thevessel is formed with a flow divider 15. A substantially verticaldistribution edge 16 on the front of this flow divider 15 is located onthe central line of the agitator 11 at a distance form the wall of thevessel portion 10. Two arc-shaped substantially vertical surfaces 17extend, one in each direction, from the distribution edge 16 outwardlyto the vessel wall, which these surfaces 17 join substantiallytangentially. The surfaces 17 are symmetrical as regards thedistribution edge 16 and are defined upwardly by an inclined plane 18forming an angle v with the vessel wall.

The arc-shaped surfaces 17 are preferably cylindrical with a radius rwhich is between about 20 and 25% of the diameter D of the vesselportion 10. The center axis of each of the arc-shaped surfaces 17 andthe distribution edge 16 should be located in the opposed half of thevessel portion 10 in relation to the agitator 11, but the distancebetween that center axis and the distribution edge and the imaginaryplane, respectively, dividing the vessel portion 10 into two halves,should be less than about 20% of the diameter D.

The height h of the distribution edge 16 should be from about 10 to 20%of the diameter D, measured from the vessel bottom. The highest pointwhere the inclined plane 18 joins the wall of the vessel portion 10should be located at a height H above the vessel bottom, where H lies inthe interval of from about 40 to 60% of the diameter D. The angle vdetermined by the difference between the heights h and H should be about45°.

Due to the design of the lower portion 10 of the vessel provided with aflow divider 15, the throw length of the agitator 11 is shortened and atthe same time the pulp flow is divided into two partial flows of equalsize. These partial flows flow back along the vessel wall, and then backto the suction side of the agitator 11 where the inclined plane 18simultaneously produces a certain upward deflection. The pulp flowdirected in this manner yields very effective mixing and requires lessenergy supply than mixing arrangements which have heretofore beenutilized.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

I claim:
 1. A mixing device for mixing a processing agent with asuspension comprising a mixing vessel having an inner surface andincluding a lower cylindrical portion having a diameter, an agitatormounted with respect to said inner surface of said mixing vessel forcreating a flow of said suspension across said mixing vessel, processingagent supply means for supplying said processing agent to said flow ofsaid suspension across said mixing vessel, and a flow divider mountedwith respect to said inner surface of said mixing vessel at a locationsubstantially opposite to the location of said agitator, said flowdivider comprising a substantially vertical front distribution edgespaced from said inner surface of said mixing vessel and a pair ofarcuate front surfaces extending from said front distribution edge tosaid inner surface of said mixing vessel on opposite sides of said frontdistribution edge, said pair of arcuate front surfaces including anupper surface defining an inclined plane with respect to said innersurface of said mixing vessel.
 2. The mixing device of claim 1 whereinsaid pair of arcuate front surfaces are substantially vertical.
 3. Themixing device of claim 1 wherein said suspension comprises a pulpsuspension.
 4. The mixing device of claim 1 wherein said pair of arcuatefront surfaces extend to said inner surface of said mixing vesselsubstantially tangentially.
 5. The mixing device of claim 1 wherein saidfront distribution edge is directly opposite said agitator.
 6. Themixing device of claim 1 wherein said front distribution edge is locatedon a diameter of said mixing vessel, and said pair of arcuate frontsurfaces comprise cylindrical surfaces having a predetermined radius. 7.The mixing device of claim 6 wherein said predetermined radius isbetween about 20 and 25% of said diameter of said mixing vessel.
 8. Themixing device of claim 1 wherein said front distribution edge has aheight, said height being between about 10 and 20% of said diameter ofsaid mixing vessel.
 9. The mixing device of claim 8 wherein said uppersurface of said pair of arcuate front surfaces has a maximum height,said maximum height being between about 40 and 60% of said diameter ofsaid mixing vessel.
 10. The mixing device of claim 1 wherein said innersurface of said mixing vessel includes a bottom surface, said bottomsurface being substantially horizontal whereby said agitator creates aflow of said suspension across said mixing vessel to said flow dividerwhich is substantially unobstructed therebetween.